Upscaling of Slug Test Hydraulic Conductivity Using Discrete Fracture Network Modelling in Granitic Aquifers

Abstract

The Indian sub-continent is underlain by hard rocks aquifers that are devoid of primary porosity and occupy more than two thirds of the landmass. These aquifers are highly vulnerable to pollution and resource depletion because they are the most heavily exploited by the population for agriculture, industry and domestic needs. These hard rocks aquifers, in general, consist of three layers: the weathered zone that can be considered as a porous media, the fissured/fractured zone, which is heterogeneous, and the fresh basement which is generally devoid of any openings unless and until some deep seated tectonic fractures are present. Aquifers in such geological settings are, therefore, of very variable quality, inherently to the heterogeneous nature of the fracture networks. Due to the adaptation of the latest drilling technology in India during the last few decades, ground water has been exploited on a large scale. But this uncontrolled exploitation of the resource has resulted in an alarming decline in water levels. The characterization of the flow and storage of ground water in these systems is a challenging task since flow and transport processes are very different from those occurring in the porous matrix. Furthermore there is an extremely high degree of contrast between the hydraulic conductivity of the fractures within short distances. An estimation of the groundwater resources is only possible through an estimation of flow and storage parameters in the fracture systems but it is anticipated that the responses of pumping tests performed in well field cannot be analyzed through classical aquifer-testing methods that assume a homogeneous aquifer.